As devices used to recognize vessels on the water, there have been conventionally known a radar detection system using radar and equipped on an own vessel and an Automatic Identification System based on information transmitted from target vessels in addition to visual monitoring by a person on the bridge.
When using the visual monitoring, the person on the bridge acquires a target vessel in three dimensions, and sensuously recognizes relative position information of the target vessel based on the direction and distance of the target vessel from the own vessel. However, when the target vessel is located far away, the person on the bridge may not correctly acquire the depth, i.e. the distance between the own and target vessels. When using radar, it is possible to acquire the relative position information of the target vessel based on the direction and distance of the target vessel from the own vessel with markedly higher accuracy in comparison with the above visual monitoring of the relative position information. However, due to the characteristics of the radar waves, it may not possible in some cases to acquire a target vessel with an insufficient reflection intensity of the radar waves. Further, when using the Automatic Identification System, the relative position information of the target vessel based on the direction and distance of from the own vessel depends on the type and reliability of information transmitted from the target vessel.
On the other hand, when taking update frequency of the information relating to the target vessel into account, while the visual information appears to be collected continuously by the person on the bridge, the collection of visual information is only continuous for a particular vessel to which the person on the bridge pays attention, and the visual information on other target vessels is updated at undetermined interval. In addition, when using radar, the interval of the information update depends on a rotation speed of a radar antenna. Furthermore, when using the Automatic Identification System, provided that the target vessel transmits information at a predetermined update interval in accordance with regulation, the interval of update varies significantly depending on the speed and the state of the target vessel, from the vessel on the berth to the vessel under way on fast track.
As described above, various relative position identifying devices such as the visual organ as the device for identifying a relational position of a target vessel represented by the direction and distance from the own vessel, the radar, and the Automatic Identification System, provide information with different range and quality at a different update interval depending on the type of the relative position identifying device. Therefore, when attempting to collect the relative position information of the target vessel using these devices separately and simultaneously, the person on the bridge may encounter a situation in which it is not possible to immediately determine which piece of relative position information acquired by one identification device for one target vessel corresponds to a piece of relative position information acquired by a different identification device for the target vessel. In particular, in a situation in which there are a number of vessels densely under way within a visual field of the person on the bridge, it becomes even more difficult to determine if the target vessel acquired by one identification device is the same vessel as the one acquired by another identification device. This poses a very serious problem in view of ensuring the secure navigation of vessels (see Patent Document 1).
[Patent Document 1]
Japanese Patent Application No. 2003-289764
An object of the present invention is to provide a vessel monitoring system that has a display unit to display an Obstacle Zone by Targets, based on a course and a speed of a target vessel and a course and a speed of an own vessel, in a case in which the course of the own vessel is changed to an arbitrary direction, the Obstacle Zone by Targets indicating a region of locations where the own vessel may reach at the same time as the target vessel with equal to or more than a predetermined probability, and, in a trial navigation by provisionally setting a value of the speed of the own vessel arbitrarily, immediately display an OZT corresponding to the arbitrarily and provisionally set value of the speed of the own vessel.